January 30 Colloquium

Kun Zhao, University of California, Los Angeles

From Colloids to Bacteria:Anisotropy in Self-Organizing Systems at the Mesoscopic Scale

Abstract: Many complex mesoscopic systems, ranging from inorganic colloids to active biological cells, exhibit a rich variety of pattern-forming behavior. In this talk, I will show you how anisotropy in two model systems, anisotropic shaped colloids and bacterial communities, affect complex pattern formation. During the directed self-assembly of colloidal systems, shape anisotropy can greatly influence resulting structures. We have developed a technique called roughness controlled depletion attraction which allows us to probe the phase space of 2D Brownian systems for a variety of anisotropic shapes such as triangles, squares, and other polygons. We have discovered several unanticipated effects, such as local symmetry breaking in a triatic liquid crystal phase of uniform triangles. Anisotropy also plays a large role in the formation of bacterial communities called biofilms. Biofilms are a major human health hazard as well as being an impediment in many industrial and medical settings. By using condensed matter techniques, we present for the first time the dynamics of colony formation at early stages of biofilm development for Pseudomonas aeruginosa. We found that Pseudomonas aeruginosa does not follow an isotropic random walk as commonly assumed, but instead obeys a new form of polysaccharide-guided dynamics such that the distribution of surface.